Circuit arrangement for switching a mobile radio transmitter between two modulation modes

ABSTRACT

A circuit is provided for regulating operation of a transmitter of a mobile communication terminal, which runs in the EDGE and GMSK modulation modes. The inventive circuit includes a power amplifier supplying an output signal for an antenna of the mobile communication terminal; a phase regulator that is provided with a phase comparator to which a setpoint signal for the output signal of the power amplifier is fed, and a voltage-controlled oscillator adjusting the phase position of the output signal of the power amplifier, the phase regulator regulating the phase position of the output signal of the power amplifier; an amplitude-regulating device that is provided with an amplitude comparator to which the setpoint signal for the output signal of the power amplifier is fed, and a battery-powered battery-voltage modulator adjusting the amplitude of the output signal of the power amplifier, the amplitude-regulating device regulating the amplitude of the output signal of the power amplifier; and a feedback line feeding an actual measured value for the output signal of the power amplifier back to the phase comparator and the amplitude comparator, the feedback line being provided with an adjustable amplifier which is controlled by a baseband chip and sets an output power of the antenna. The inventive circuit includes a changeover switch which is wired in such a way that it connects an input of the battery-voltage modulator to an output of the amplitude comparator in a first position for the EDGE mode while connecting an input of the battery-voltage modulator to an output of the power amplifier in a second position for the GMSK mode, the connection being made via the adjustable amplifier in both positions.

BACKGROUND OF THE INVENTION

The present invention relates to a circuit for controlling operation ofa transmitter in a mobile communication terminal, which transmitter isdesigned for the modulation modes EDGE and GMSK, having:

a power amplifier which delivers an output signal for an antenna on themobile communication terminal;

a phase controller, which has a phase comparator, to which a nominalsignal for the output signal from the power amplifier is supplied, and avoltage controlled oscillator for aligning the phase of the outputsignal from the power amplifier, for controlling the phase of the outputsignal from the power amplifier;

an amplitude controller, which has an amplitude comparator, to which thenominal signal for the output signal from the power amplifier issupplied, and a battery voltage modulator, powered by a battery, foraligning the amplitude of the output signal from the power amplifier,for controlling the amplitude of the output signal from the poweramplifier; and

a feedback line for feeding back a present measured value for the outputsignal from the power amplifier to the phase comparator and to theamplitude comparator, which feedback line has an adjustable amplifier,controlled by a baseband chip using a control signal, for setting anoutput power for the antenna. Such a circuit is used in the prior artboth for the modulation mode EDGE and for the modulation mode GMSK, withthe circuit being invariable with regard to such modulation modes. Theway in which the known circuit works is explained below with referenceto FIG. 2. It will be emphasized in this regard that a transmitterequipped with such a circuit is referred to, generally, as a “polar looptransmitter.”

As will be seen in FIG. 2, a nominal voltage signal U_(s) is suppliedboth to an input on a phase comparator 1 and to an input on an amplitudecomparator 2. Respective second inputs on the phase comparator 1 and onthe amplitude comparator 2 have an output voltage U_(a) applied to them,specifically with the interposition of an adjustable amplifier 4 whichdetermines an attenuation for the output voltage Ua and hence a gainfactor U_(a)/U_(s) for the amplitude control loop. The attenuation ofthe controllable amplifier 4 can, thus, be used to set the output powerdelivered to the antenna.

The adjustable amplifier 4 is controlled by a baseband chip in a mobilecommunication terminal to which the circuit belongs, with a controlsignal R applied to the adjustable amplifier 4 being able to be chosenon the basis of a power requirement from a remote station for the mobilecommunication terminal, such as a base station in a mobile radionetwork.

An output signal from the phase comparator 1 is supplied to a voltagecontrolled oscillator 5 whose output signal U_(in) is applied to aninput on the power amplifier 3 and aligns the phase of the output signalU_(a) with the phase of the nominal voltage U_(s).

An output signal from the amplitude comparator 2, which is typically anintegrating error amplifier in practice, is applied to an input on abattery voltage modulator 6 which is powered by a battery U_(batt) or astorage battery in the mobile communication terminal. An output signalfrom the battery voltage modulator 6 is used for aligning the amplitudeof the voltage signal U_(a) with the amplitude of the nominal signalU_(s), specifically taking into account the attenuation by theadjustable amplifier 4.

In the circuit shown in FIG. 2, a feedback line runs from the output ofthe power amplifier 3 for the output voltage U_(a) via the adjustableamplifier 4 to the respective inputs of the phase comparator 1 and theamplitude comparator 2.

The battery voltage modulator 6 directly influences a supply voltageU_(c) for the power amplifier 3 and, thus, an envelope for the outputvoltage signal U_(a) from the power amplifier 3.

The circuit explained above has no kind of variability for the purposeof optimizing this operation with respect to various modulation modes,such as EDGE and GMSK. These modulation modes are readily known toexperts in the field of mobile radio technology. For details, referenceis made to the specialist book “Mobilfunknetze und ihre Protokolle1”[Mobile radio networks and their protocols 1] by B. Walke, thirdedition, published by Verlag B. G. Teubner, 2001.

The described circuit based on the prior art, which is used forlinearizing the power amplifier 3, has the following drawback when usedfor either the EDGE or GMSK modulation modes: to ensure error-freeoperation of the transmitter, the power P_(a) delivered to an antenna 7by the power amplifier 3, and thus the output voltage U_(a), must alwaysbe below its maximum deliverable output power P_(max). If a drop in theavailable storage battery voltage causes, by way of example, the maximumdeliverable output voltage U_(max) to fall below the value which is tobe chosen for the output voltage U_(a) on the basis of the control, thenthe amplitude controller reaches its control limit. In this unwantedoperating state, control loop instabilities and saturation effects canresult in impairment of the switching and modulation spectrum. Timingproblems also may arise, since when its control limit has been reachedthe amplitude comparator requires a certain time in order to leavesaturated operation; for example, if the output power P_(a) needs to bebrought down at the end of a transmission time slot. As such, both theappearance and the leaving of the control limit results in unwantedeffects in the time profile for the output power P_(a) as well as in theswitching spectrum, where even the prescribed power boundaries forrelevant mobile radio standards can be infringed.

To avoid the control limit, appropriate dimensioning of the poweramplifier 3 has been used, to date, to provide a sufficiently highreserve for the available output power P_(max). However, this results inhigh component costs and/or premature disconnection of the mobilecommunication terminal as a result of faster consumption of the storagebattery capacity. The latter drawback can be overcome only by using alarger and more expensive storage battery.

Against this background, the present invention is directed toward acircuit, as cited at the outset, wherein it is economically moreefficient for the two modulation modes EDGE and GMSK.

SUMMARY OF THE INVENTION

Such object is achieved for the above-described circuit by virtue of achangeover switch being provided which connects an input on the batteryvoltage modulator to an output on the amplitude comparator in a firstposition for the EDGE mode and, in a second position for the GMSK mode,the control signal for the adjustable amplifier is applied directly tothe input of the battery voltage modulator.

The effect achieved by using the changeover switch is that the amplitudecontroller is not used in the transmitter's GMSK mode. Instead, thecontrol signal for the adjustable amplifier is supplied directly to thebattery voltage modulator so that it is used as control signal for thebattery voltage modulator. In this way, in the GMSK mode, the controllimit for the amplitude controller is effectively prevented from beingreached. Dispensing with the amplitude control can be accepted becausethe GMSK modulation mode has no provision for amplitude modulation, butrather only for phase modulation.

The adjustable amplifier can bring about a raising or lowering of theoutput voltage and, accordingly of the output power from the poweramplifier, with the adjustable amplifier's setting needing to becontrolled with sufficient accuracy.

Preferably, a second changeover switch is provided which is connectedsuch that it connects the input of the phase comparator to the output ofthe power amplifier in a first position and to an output of theoscillator in the second position. In this case, it is preferred thatthe second changeover switch adopt its first position for the EDGE mode,while the second changeover switch adopt its second position for theGMSK mode. The reason for this is that there is amplitude modulation inEDGE mode. Since a phase response in the power amplifier is normallyamplitude dependent, the output signal is highly phase distorted. Toeliminate this error, the phase error in the output voltage U_(a) needsto be corrected by the phase controller.

In the GMSK mode, this correction is not necessary. In this case, it issufficient to return the output signal from the oscillator.

This has the advantage that the phase controller's decoupling from thepower amplifier results in it being relatively insensitive tointerference signals received by the antenna, wherein otherwisenecessary additional measures for suppressing interference signals, suchas connectable attenuating elements in a line from the power amplifierto the antenna, can be dispensed with.

Another advantage of the present invention is that the battery voltagemodulator already provided in the prior art is used as an actuatingelement for the output power from the power amplifier. By providing thetwo changeover switches, it is possible, without any further complexityin terms of components as compared with the known circuit arrangement,to choose a respectively optimized transmitter mode for the twomodulation modes GMSK and EDGE.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the Figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a circuit for a polar loop transmitter which can beswitched between an EDGE modulation mode and a GMSK modulation mode.

FIG. 2 shows a circuit for a polar loop transmitter based on the priorart.

DETAILED DESCRIPTION OF THE INVENTION

The inventive circuit contains the same main components as the circuitbased on the prior art; namely, a phase comparator 11, an amplitudecomparator 12, a power amplifier 13, an adjustable amplifier 14, avoltage controlled oscillator 15, a battery voltage modulator 16 and anantenna 17.

Both the phase comparator 11 and the amplitude comparator 12 aresupplied with a nominal voltage U_(s) as input signal. In addition, apresent measured value for the output voltage U_(a) from the poweramplifier 13 is fundamentally fed back to respective inputs on the phasecomparator 11 and on the amplitude comparator 12. In contrast to theprior art, however, the present invention makes provision for achangeover switch S1 which can be switched between a first and a secondposition.

The position of the switching S1 governs which signal is applied to aninput on the battery voltage modulator 16. In GMSK mode, the switch S1adopts its first position, in which a control signal R1 for theadjustable amplifier 14 is applied directly to an input on the batteryvoltage modulator 16 by the switch S1, whereby, in this instance ofoperation, there is no amplitude control for the output signal U_(a)from the power amplifier 13. Instead, the control signal R1 for theadjustable amplifier 14 acts directly as control signal for the batteryvoltage modulator 16. In this way, a control limit for the amplitudecontroller is avoided, since there is no amplitude control in GMSK mode.

If the transmitter, which is part of a mobile communication terminal, isoperated with the EDGE modulation mode, the switch S1 adopts its secondposition, in which an output signal from the amplitude comparator 12 isapplied directly to the input of the battery voltage modulator 16. Inthis position of the changeover switch S1, amplitude control is used inthe same way as in the circuit shown in FIG. 2, which corresponds to theprior art.

In addition, the circuit shown in FIG. 1 contains a second changeoverswitch S2, which governs which signal is applied to that input of thephase comparator 11 whose signal value needs to be compared with thenominal voltage signal U_(s). In the EDGE modulation mode, thechangeover switch S2 adopts a first position, in which the outputvoltage or the output signal from the power amplifier 13 is fed back tothe respective inputs of the phase comparator 11 and the amplitudecomparator 12, which is an integrating error amplifier, so that controlfor the phase of the output voltage signal U_(a) using the voltagecontrolled oscillator 5 takes place in the same way as in the circuitshown in FIG. 2, which corresponds to the prior art.

By contrast, in the GMSK modulation mode, the changeover switch S2adopts a second position, in which an output signal from the oscillator15 is fed back directly to an input on the phase comparator 11, with thesignal applied to this input being compared with the voltage nominalsignal Us using the phase comparator 1.

In view of the above explanations, it becomes clear that FIG. 1 showsthe changeover switches S1 and S2 in such positions as are necessary foroperation of the transmitter when a GMSK modulation mode is effective.

In comparison with the circuit based on the prior art, the circuit shownin FIG. 1 likewise has a feedback line which runs from an output on thepower amplifier 13 via the adjustable amplifier 14 and the changeoverswitch S2 to the relevant inputs of the phase comparator 11 and theamplitude comparator 12. The inventive circuit, however, is providedwith an additional feedback line which runs from an output on theoscillator 15 to the changeover switch S2. A further additional line,whose path supplies the control signal for the adjustable amplifier(VGA; Variable Gain Amplifier) 14 (EDGE) or the battery voltagemodulator 16 (GMSK), runs from the adjustable amplifier 14 to thechangeover switch S1.

The advantages of the present invention become particularly clear whenthe output powers stipulated in respective standards for GMSK and EDGEare considered. The maximum output power for GMSK is +33 dBm. Therelevant value for the EDGE modulation mode is +30 dBm_(PEP). In thisregard, a multimode appliance, which is provided for both GMSK mode andfor EDGE mode, already has an output power reserve of 3 dB for EDGEmode, which is normally sufficient for error-free operation of thetransmitter in EDGE mode.

An even higher reserve for the GMSK mode is now avoided by virtue of thechangeover switch S1 being provided, whereby the battery voltagemodulator 16 is actuated directly by an output signal from theadjustable amplifier 14. The transmitter's output power can be setsimply by controlling the battery voltage modulator 16 with sufficientaccuracy.

Although the present invention has been described with reference tospecific embodiments, those of skill in the art will recognize thatchanges may be made thereto without departing from the spirit and scopeof the present invention as set forth in the hereafter appended claims.

1. A circuit for controlling operation of a transmitter in a mobilecommunication terminal, the transmitter being designed for both EDGE andGMSK modulation modes, the circuit comprising: a power amplifier fordelivering an output signal, via an output of the power amplifier, foran antenna on the mobile communication terminal; a phase controller forcontrolling a phase of the output signal from the power amplifier,wherein the phase controller includes a phase comparator with an inputto which a nominal signal for the output signal from the power amplifieris supplied, and further including a voltage controlled oscillator foraligning the phase of the output signal from the power amplifier; anamplitude controller for controlling an amplitude of the output signalfrom the power amplifier, wherein the amplitude controller includes anamplitude comparator to which the nominal signal for the output signalfrom the power amplifier is supplied, and further including a batteryvoltage modulator, powered by a battery, for aligning the amplitude ofthe output signal from the power amplifier; a feedback line for feedingback a present measured value for the output signal from the poweramplifier to both the phase comparator and the amplitude comparator,wherein the feedback line includes an adjustable amplifier, controlledby a baseband chip using a control signal, for setting an output powerfor the antenna; and a changeover switch for connecting an output on theamplitude comparator to an input on the battery voltage modulator in afirst position for the EDGE modulation mode, and for connecting thecontrol signal for the adjustable amplifier directly to the input of thebattery voltage modulator in a second position for the GMSK modulationmode.
 2. A circuit for controlling operation of a transmitter in amobile communication terminal as claimed in claim 1, wherein theadjustable amplifier raises and lowers the amplitude of the outputsignal from the power amplifier.
 3. A circuit for controlling operationof a transmitter in a mobile communication terminal as claimed in claim1, further comprising a second changeover switch for connecting theoutput of the power amplifier to the input of the phase comparator in afirst position, and for connecting an output of the voltage controlledoscillator to the input of the phase comparator in a second position. 4.A circuit for controlling operation of a transmitter in a mobilecommunication terminal as claimed in claim 3, wherein the secondchangeover switch is in the first position for the EDGE modulation mode.5. A circuit for controlling operation of a transmitter in a mobilecommunication terminal as claimed in claim 3, wherein the secondchangeover switch is in the second position for the GMSK modulationmode.